I woke up last night at 3:30am freezing and found that the zone-valve (1 of 3) was OPEN but the circulator pump would not operate for that zone only.

I verified that the circulator pump was OK and responding correctly to the other 2 zones by turning up those thermostats. I also found that the zone-valve was functioning properly because this zonevalve happens to make ticking sounds constantly when opened (very easy to hear).

Now if the thermostat is OK, (zone-valve opened) and the circ pump is OK, and the burner and everythign else is OK, what would cause the circulator pump to not activate on that one zone only?

As a temporary fix, I turned up the thermostat on another zone just to get the circ pump running and we did have heat for the rest of the morning (which proves everything else is working).

Could the Honeywaell L8124A Aquastat Relay be bad? I dont think so because it cannot tell the difference between zones, right?

Thanks in advance, I really don't know what it could be.